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. Second, while the narrowness of the jets is maintained by eddy momentum fluxes (as has long been understood), their equatorward migration is a response to the eddy heat fluxes, which act to reduce the baroclinicity on the poleward flank of the jets and increase it on the equatorward flank. We speculate that this behavior is ultimately determined by the latitudinal gradient of the background static stability. The structure of the paper is as follows. A cursory description of the model and its time
. Second, while the narrowness of the jets is maintained by eddy momentum fluxes (as has long been understood), their equatorward migration is a response to the eddy heat fluxes, which act to reduce the baroclinicity on the poleward flank of the jets and increase it on the equatorward flank. We speculate that this behavior is ultimately determined by the latitudinal gradient of the background static stability. The structure of the paper is as follows. A cursory description of the model and its time
results, we will also pay special attention to changes in eddy fluxes that accompany variations in the zonal mean. While the annular modes themselves are zonally symmetric, eddy feedback plays a critical role in maintaining the patterns. Diagnoses of both reanalysis and model results indicate a connection between the annular wind anomalies and eddy activity ( Limpasuvan and Hartmann 2000 ). Lorenz and Hartmann (2001 , 2003 found that this relationship between eddies and mean flow represents a
results, we will also pay special attention to changes in eddy fluxes that accompany variations in the zonal mean. While the annular modes themselves are zonally symmetric, eddy feedback plays a critical role in maintaining the patterns. Diagnoses of both reanalysis and model results indicate a connection between the annular wind anomalies and eddy activity ( Limpasuvan and Hartmann 2000 ). Lorenz and Hartmann (2001 , 2003 found that this relationship between eddies and mean flow represents a
tropospheric weather conditions ( Thompson and Wallace 2001 ; Baldwin et al. 2003 ). Also, polar vortex variations have been linked to regional variability in column ozone and incoming UV flux at the earth’s surface ( Karpetchko et al. 2005 ). Although annular modes occur over a wide range of time scales (weeks to decades), there has been a substantial focus on subseasonal variability (e.g., Limpasuvan et al. 2004 ; McDaniel and Black 2005 , hereafter MB ) and long-term trends ( Thompson and Solomon
tropospheric weather conditions ( Thompson and Wallace 2001 ; Baldwin et al. 2003 ). Also, polar vortex variations have been linked to regional variability in column ozone and incoming UV flux at the earth’s surface ( Karpetchko et al. 2005 ). Although annular modes occur over a wide range of time scales (weeks to decades), there has been a substantial focus on subseasonal variability (e.g., Limpasuvan et al. 2004 ; McDaniel and Black 2005 , hereafter MB ) and long-term trends ( Thompson and Solomon
generation: to the extent that wave activity radiates away from this source, eddy momentum fluxes converge into this region, and this momentum is removed from the atmosphere by surface friction through the generation of surface westerlies. Using a global two-level primitive equation model, R97 argues that a reduction in surface drag results, first of all, in an enhancement of the barotropic component of the flow, with relatively modest changes in the baroclinic component. But these changes in
generation: to the extent that wave activity radiates away from this source, eddy momentum fluxes converge into this region, and this momentum is removed from the atmosphere by surface friction through the generation of surface westerlies. Using a global two-level primitive equation model, R97 argues that a reduction in surface drag results, first of all, in an enhancement of the barotropic component of the flow, with relatively modest changes in the baroclinic component. But these changes in
and Polvani 2007 ), and the evolution of stratospheric final warming (SFW) events ( Black et al. 2006 ). In the above-mentioned studies as well as in many other studies, the analysis of the wave forcing of the stratospheric polar vortex was performed within the traditional framework of Eliassen–Palm (EP) flux. However, the use of the EP flux as a diagnostic tool of wave propagation is strictly valid only in the case of small-amplitude waves. Frequent usage is also made of other concepts associated
and Polvani 2007 ), and the evolution of stratospheric final warming (SFW) events ( Black et al. 2006 ). In the above-mentioned studies as well as in many other studies, the analysis of the wave forcing of the stratospheric polar vortex was performed within the traditional framework of Eliassen–Palm (EP) flux. However, the use of the EP flux as a diagnostic tool of wave propagation is strictly valid only in the case of small-amplitude waves. Frequent usage is also made of other concepts associated
quantities defined as linear Rossby waves for Ω = 400 and Ω = 10 000, respectively. Note that these figures are equatorially symmetric because of the ensemble-mean process utilized, but we have kept both hemispheres to enable us to clearly recognize the contrast of behaviors between the polar caps and the other regions. The plotted quantities are wave activity (pseudo–angular momentum associated with Rossby waves) cos φ /(2 β̂ ), the latitudinal component of wave activity flux cos φ , its divergence
quantities defined as linear Rossby waves for Ω = 400 and Ω = 10 000, respectively. Note that these figures are equatorially symmetric because of the ensemble-mean process utilized, but we have kept both hemispheres to enable us to clearly recognize the contrast of behaviors between the polar caps and the other regions. The plotted quantities are wave activity (pseudo–angular momentum associated with Rossby waves) cos φ /(2 β̂ ), the latitudinal component of wave activity flux cos φ , its divergence
much of Greenland, and its massive ice cap, a remnant of the last glaciation, is a monument to poleward atmospheric moisture flux, which is concentrated in the Atlantic sector at these latitudes. With a height averaging about 1.5 km and reaching greater than 3.5 km, roughly the 650-hPa level, and with relatively high volume and steep southern termination, its potential effect on the general circulation is great. Yet, lying between 60° and 83°N latitude, it is north of the maximum zonally averaged
much of Greenland, and its massive ice cap, a remnant of the last glaciation, is a monument to poleward atmospheric moisture flux, which is concentrated in the Atlantic sector at these latitudes. With a height averaging about 1.5 km and reaching greater than 3.5 km, roughly the 650-hPa level, and with relatively high volume and steep southern termination, its potential effect on the general circulation is great. Yet, lying between 60° and 83°N latitude, it is north of the maximum zonally averaged
cycle. The whole system is integrated forward on a parallel computer, one processor being employed for each side of the atmospheric cube: one for the ocean and one to handle coupling. The system can carry out 1000 yr of synchronous coupled integration in two weeks of dedicated integration. Fluxes of momentum, heat, and freshwater are exchanged every hour (the ocean model time step). The model, launched from a state of rest with temperature and salinity distributions taken from a zonal-average ocean
cycle. The whole system is integrated forward on a parallel computer, one processor being employed for each side of the atmospheric cube: one for the ocean and one to handle coupling. The system can carry out 1000 yr of synchronous coupled integration in two weeks of dedicated integration. Fluxes of momentum, heat, and freshwater are exchanged every hour (the ocean model time step). The model, launched from a state of rest with temperature and salinity distributions taken from a zonal-average ocean
random variations in the eddy vorticity fluxes. As the integral of eddy fluxes, the zonal flow exhibits greater power on lower frequencies than the eddies. If one assumes that the eddy fluxes are white in time (at least on time scales longer than 10 days) and that the damping of the large-scale anomalies is linear, the NAO and annular modes have a red spectrum as characterized by an autoregressive process of first order (AR-1) or, as it is also known, an Ornstein–Uhlenbeck process. There is evidence
random variations in the eddy vorticity fluxes. As the integral of eddy fluxes, the zonal flow exhibits greater power on lower frequencies than the eddies. If one assumes that the eddy fluxes are white in time (at least on time scales longer than 10 days) and that the damping of the large-scale anomalies is linear, the NAO and annular modes have a red spectrum as characterized by an autoregressive process of first order (AR-1) or, as it is also known, an Ornstein–Uhlenbeck process. There is evidence
; the width of each band remains almost unchanged afterward, although a slight change in its magnitude and shape continues on top of the slowly growing small westerly bias. The formation of an easterly circumpolar jet, which appears around the southern pole in the case of Fig. 4e , proceeds gradually and continuously. The poleward accumulation of easterly momentum from the mid- and low latitudes is exemplified in the cumulative eddy angular momentum flux in Fig. 5e (the details of Fig. 5 are
; the width of each band remains almost unchanged afterward, although a slight change in its magnitude and shape continues on top of the slowly growing small westerly bias. The formation of an easterly circumpolar jet, which appears around the southern pole in the case of Fig. 4e , proceeds gradually and continuously. The poleward accumulation of easterly momentum from the mid- and low latitudes is exemplified in the cumulative eddy angular momentum flux in Fig. 5e (the details of Fig. 5 are
